1. Field of the Invention
This invention relates to devices such as organic electronic devices and methods for forming such devices.
2. Description of Related Art
Semiconducting conjugated polymer thin-film transistors (TFTs) have recently become of interest for applications in cheap, logic circuits integrated on plastic substrates (C. Drury, et al., APL 73, 108 (1998)) and optoelectronic integrated devices and pixel transistor switches in high-resolution active-matrix displays (H. Sirringhaus, et al., Science 280, 1741 (1998), A. Dodabalapur, et al. Appl. Phys. Lett. 73, 142 (1998)). In test device configurations with a polymer semiconductor and inorganic metal electrodes and gate dielectric layers high-performance TFTs have been demonstrated. Charge carrier mobilities up to 0.1 cm2/Vs and ON-OFF current ratios of 106–108 have been reached, which is comparable to the performance of amorphous silicon TFTs (H. Sirringhaus, et al., Advances in Solid State Physics 39, 101 (1999)).
One of the advantages of polymer semiconductors is that they lend themselves to simple and low-cost solution processing. However, fabrication of all-polymer TFT devices and integrated circuits requires the ability to form lateral patterns of polymer conductors, semiconductors and insulators. Various patterning technologies such as photolithography (WO 99/10939 A2), screen printing (Z. Bao, et al., Chem. Mat. 9, 1299 (1997)), soft lithographic stamping (J. A. Rogers, Appl. Phys. Lett. 75, 1010 (1999)) and micromoulding (J. A. Rogers, Appl. Phys. Lett. 72, 2716 (1998)), as well as direct ink-jet printing (H. Sirringhaus, et al., UK 0009911.9) have been demonstrated.
Many direct printing techniques are unable to provide the patterning resolution that is required to define the source and drain electrodes of a TFT. In order to obtain adequate drive current and switching speed channel lengths of less than 10 μm are required. In the case of inkjet printing the achievable resolution is limited to 20–50 μm by accidental variations of the droplet flight direction caused by changing ejection conditions at the nozzle and by the uncontrolled spreading of the droplets on the substrate.
This resolution limitation has been addressed by printing onto a prepatterned substrate containing regions of different surface free energy (H. Sirringhaus et al., UK 0009915.0). When water-based ink droplets of a conducting polymer are printed onto a substrate containing narrow regions of repelling, hydrophobic surface structure the spreading of droplets can be confined and transistor channels with a channel length of only 5 □m can be defined without accidental short between source and drain electrodes. The hydrophobic barrier can be defined in several ways, for example, by photolithography of a hydrophobic polymer or by soft lithographic stamping of a self-assembled monolayer.